1. Field of the Invention
The present invention relates to an electronic cassette for use in radiography.
2. Description Related to the Prior Art
An electronic cassette has been widely used in medical radiography, for example, in X-ray photography. The electronic cassette is a portable X-ray image detector provided with an built-in image detector (also referred to as a flat panel detector (FPD)) for detecting an X-ray image of a subject such as a patient inside a housing having a front surface on which X-rays are incident, a rear surface facing the front surface, and four side surfaces.
As shown in FIG. 1 in Japanese Patent Laid-Open Publication No. 2014-057831, an electronic cassette is set to be attachable to and detachable from a holder of an upright radiographic stand or a supine radiographic stand, such that the electronic cassette is held in a posture in which an X-ray source for irradiating X-rays and a front surface of a housing face each other. The holder has a front plate for covering the front surface of the housing and a rear plate for covering a rear surface of the housing. The holder is made of an electrically-conductive material having electromagnetic wave shielding properties.
Further, in X-ray photography, since scattered rays are generated upon transmission of X-rays through a subject, a grid for removing the scattered rays is used in some cases. There is a grid detachably attached to an electronic cassette externally (hereinafter referred to as external grid) (see Utility Model Registration No. 3137548 and Utility Model Registration No. 3144690). The external grid is not attached to an electronic cassette in the case where the electronic cassette is set to a holder of an upright radiographic stand or a supine radiographic stand. The external grid is attached to an electronic cassette in the case where the electronic cassette is used alone for a subject lying on a bed or a subject who cannot move on his/her own such as an aged person or an emergency patient.
The external grid consists of a grid body and a holding frame for holding the grid body. The grid body is attached to the holding frame. The holding frame has a top panel for covering the front surface of the housing, and a side panel which is provided to an edge of the top panel and extends in a direction from a front-surface side of the housing to a rear-surface side thereof so as to cover part of a side surface of the housing. The holding frame is made of an electrically-conductive material having electromagnetic wave shielding properties in the same manner as the holder of the radiographic stand.
There is an electronic cassette, which is provided with a wireless communication section for wireless communication with an external device such as a control device for controlling operation of the electronic cassette and a battery for supplying electricity to activate the electronic cassette, such that the electronic cassette can be used without a cable. For example, United States Patent Application Publication No. 2012/0228499 corresponding to Japanese Patent Laid-Open Publication No. 2011-112923 discloses an electronic cassette incorporating an antenna of a wireless communication section provided at a surface facing an X-ray incident surface of an image detector in a housing.
The housing is made of an electrically-conductive material having electromagnetic wave shielding properties in the same manner as a holder of an radiographic stand and a holding frame of an external grid in order to prevent electromagnetic noise from entering the electronic cassette and prevent electromagnetic noise from being emitted from the electronic cassette to the outside. According to United States Patent Application Publication No. 2012/0228499, the antenna is incorporated in the housing as descried above, and an antenna opening through which a radio wave is transmitted is formed on a rear surface or a side surface of the housing, such that transmission/reception of the radio wave through the antenna can be performed. According to Japanese Patent Laid-Open Publication No. 2014-057831, a cover having radio wave transmission properties is attached to an antenna opening.
However, there are the following problems in the case where the antenna opening is formed on the rear surface or the side surface of the housing as disclosed in Japanese Patent Laid-Open Publication No. 2014-057831.
In the case where the antenna opening is formed on the rear surface of the housing, when the electronic cassette is set to the holder of the radiographic stand, the rear plate of the holder having electromagnetic wave shielding properties blocks the antenna opening formed on the rear surface of the housing in some cases. In the case where the antenna opening is formed on the side surface of the housing, when the outer grid is attached to the housing, the side panel of the holding frame having electromagnetic wave shielding properties blocks the antenna opening formed on the side surface of the housing in some cases.
In the case where the antenna opening is blocked by a member having electromagnetic wave shielding properties such as the holder of the radiographic stand and the outer grid, the radio wave transmission properties are decreased or wireless communication speed is reduced, or even worse, the wireless communication is sometimes disconnected. Therefore, it becomes impossible to perform stable wireless communication.
Incidentally, in the case where the antenna opening is formed on not the rear surface or the side surface of the housing but a front surface of the housing, since the front surface of the housing is blocked by the front plate of the holder of the radiographic stand or the top panel of the outer grid in the similar manner as the rear surface and the side surface of the housing. Therefore, it is not appropriate to form the antenna opening on the front surface as well as the rear surface and the side surface.
In the case where the antenna opening is formed on any of the side surface, the rear surface, and the front surface, of the housing as described above, in a usage environment in which the electronic cassette is set to the holder of the radiographic stand or in which the outer grid is attached to the electronic cassette, it is impossible to perform stable wireless communication in some cases.
Thus, in the case where the antenna opening is blocked by the member having electromagnetic wave shielding properties such as the holder of the radiographic stand and the outer grid, it may be possible to improve the radio wave transmission properties at any rate by processing a portion of the member blocking the antenna opening, for example, by cutting out the portion of the member blocking the antenna opening or making a hole on the portion of the member blocking the antenna opening, such that the shape of the portion of the member blocking the antenna opening corresponds to the shape of the antenna opening. However, such processing is troublesome. Additionally, the strength of the member may be deteriorated in some cases.